Poly-V pulleys are intended to transmit high speed rotation efficiently, and are used in the rotary transmission system of automobiles and other machines. A conventional example of such poly-V pulleys made from sheet metal made is disclosed in Layed-Open Japanese Patent Application No. 57-88929.
The manufacturing method of making poly-V pulleys from sheet metal disclosed in this Layed-Open Patent Application comprises the steps of forming a cup-shaped blank by drawing a disc-shaped sheet metal material, drawing the corner part of the boundary area of the bottom wall and peripheral wall of the cup-shaped blank to form the double folded ears projecting outside the peripheral wall in an annular shape, folding the outer edge part of the peripheral wall outward to form the ears projecting outside the peripheral wall in an annular shape, corrugating the peripheral wall by pressing in the axial direction with the bottom pattern and top pattern, and flattening the corrugated portion with the inner pattern and outer pattern by pressing from both sides to increase the wall thickness of the peripheral wall, and forming by rolling a poly-V groove at the outer side of the peripheral wall of the thus thickened cup-shaped blank.
In this manufacturing method, in order to increase the thickness of the peripheral wall of the cup-shaped blank, the disc-shaped sheet metal material is once formed into a cup shape, and its peripheral wall is increased in thickness, which requires complicated forming machines and takes a long time to increasing the wall thickness and forming.
It is therefore a primary object of the present invention to present a novel manufacturing method of making poly-V pulleys of sheet metal capable of increasing the thickness of the peripheral wall of a cup-shaped blank efficiently by simple forming equipment, and products obtained by this manufacturing method.